1. Field of The Invention
The present invention relates to an optical unit coupling mechanism for coupling optical units having a plurality of mutually parallel optical paths with each other, in which use is made of a round dovetail.
2. Discussion of Related Art
The above type of optical unit coupling mechanism is commonly employed as means for coupling, for example, individual units of a stereomicroscope as shown in FIG. 11 with each other. In this stereomicroscope, the optical system is now constructed by interposing various units known as intermediate tubes (or intermediate lens barrels), for example, a photographic tube (or photographic lens barrel) 103 and a coaxial falling light illuminator 104 between a zoom lens body 101 and a binocular observation tube (or binocular lens barrel) 102 in order to comply with the user needs diversified year after year. The mechanism for coupling an intermediate tube with the zoom lens body 101, mechanism for coupling the intermediate tubes with each other and mechanism for coupling an intermediate tube with the binocular observation tube 102 generally each comprise the round dovetail disclosed as prior art in Japanese Utility Model Laid-Open No. 11084/1985. Further, Japanese Utility Model Laid-Open No. 164401/1989 discloses a stereomicroscope in which use is made of a combination of prisms and includes a drawing showing the formation of the round dovetail at a lower part of a binocular observation tube through which a pair of light beams pass.
However, the above common optical unit coupling mechanism for achieving coupling of the individual optical units with the use of the round dovetail according to the prior art has involved the following problem. In stereomicroscopes, as mentioned above, the optical system is often constructed by piling two or three intermediate tubes in order to comply with the diversified user needs. In this optical system, the effective diameter of each tube must be satisfactorily large for observing the entire visual field without the occurrence of eclipse, shading or other problem. Further, the effective diameter of the light beam must be large for increasing NA and enlarging the visual field in order to enable performance enhancement.
In the round dovetail disclosed in Japanese Utility Model Laid-Open No. 164401/1989, as shown in FIGS. 12 and 13, the structure thereof is such that fastening is effected by pressing a slant face 111 of the round dovetail. Thus, the diameter d.sub.11 of a minor diameter part 112 forming an abutting joint face is conspicuously small relative to the diameter d.sub.12 of a major diameter part 113 of the round dovetail with the result that the effective diameter d.sub.13 of the light beam is limited by the above diameter d.sub.11 of the minor diameter part 112 forming an abutting joint face. If it is intended to render the effective diameter d.sub.13 of the light beam larger than the diameter d.sub.11 of the minor diameter part 112, either the dovetail per se must be enlarged or the spacing between the right optical axis and the left optical axis must be reduced. However, enlarging the dovetail per se leads to an apparatus enlargement. Further, the spacing between the right optical axis and the left optical axis is nearly entirely determined by the internal angle of the right and left optical axes on an object side, the NA and the size of the apparatus per se, which generally ranges from 22 to 24 mm in Galilean stereomicroscopes, and changing the above spacing is difficult. Still further, the size of the dovetail and the spacing between the optical axes often cannot be changed at all for ensuring a system compatibility.